The first person animation for crouching and fire burning are sped up or slowed down by the game's framerate. A high end PC with VSync off will have strange animations, while they play slowly on a slow PC. I have attached clips of fire and crouching at 30 and uncapped framerates.
Thank you for your report!
We're actually already tracking this issue at MCPE-59122, so we will resolve and link this ticket as a duplicate.
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